The present invention generally relates to method and apparatus for providing a support deck for a mattress or a seat. The support deck of the present invention is particularly suitable for use in sofa beds although the invention need not be limited thereto. In the past, sofa bed mattress decks have been made with link fabrics or polypropylene which are attached to an outside frame with hooks or helicals. The link fabric decks have an inherent flaw because they are comprised of a grid of wires which are free to pivot or yield thus offering little resistance when a person sits or rests on the unfolded sofa bed, this effect is known in the industry as "hammocking". The sofa bed decks made from polypropylene also suffer from the same inherent flaw in that they consist of a canvas-type material attached to a frame with hooks or helicals which simply are not resilient or strong enough to provide proper support for a person sitting or resting on the sofa bed.
Another problem with the prior art is what is known in the industry as "crowning". Crowning occurs when the sofa bed mattress, after having been folded and recessed back into the sofa, is so thick as to push upwards against the sofa bed deck causing a bulge because the sofa bed deck is not strong enough to restrain the compacted mattress. This bulge then makes it impossible for seat cushions to lay flat on the sofa, a condition known in the industry as cushion "smiling". Sitting on a sofa with "smiling" cushions is also unpleasant since one sits on a firm bulge of mattress almost teetering back and forth.
The present invention involves the use of a unique interlocking grid system in a support deck in order to eliminate mattress "hammocking", "crowning" and seat cushion "smiling" in sofa beds.